Electrolysis Fantasies
Water is an ash. By chemical energetics, it is thus about the worst place to look for a bulk hydrogen source. At first glance, it seems easy enough to use electrolysis to split water into its oxygen and hydrogen components. Just apply any low dc current for bubble, bubble, toil and trouble. Full details first appeared by Michael Faraday over a century ago. And are easily found today in Britannica’s Great Books #45.
Electrolysis is certainly useful for cooling generators or petrochemical refining or precision low energy torches or lifting research balloons or making fat pretty but deadly. But nearly all of these use unstored hydrogen-on-demand and do value their hydrogen much higher than by its meager energy content.
As we’ve seen, retail electricity is worth about ten cents per kilowatt hour. Lower exergy gasoline is worth three cents per kilowatt hour. Your value of raw unprocessed hydrogen is not well established, but we do know it will certainly be a lot less than gasoline today. Because it has not yet impacted gasoline in any significant way. I feel 0.8 cents per raw hydrogen kilowatt hour can be a reasonable ballpark estimate.
In a typical situation, electrolysis takes two or more kilowatt hours of electricity worth ten cents each and converts them into one or fewer kilowatt hours of hydrogen worth less than a penny each. And that is before any fully burdened cost accounting, amortization, storage or processing. Thus… Electrolysis for bulk hydrogen energy is pretty much the same as 1:1 converting US dollars into Mexican Pesos.
At its very best, electrolysis introduces a staggering loss of exergy that dramatically reduces the quantity and value of transformed kilowatt hours of energy. Electrolysis is thus wildly unsuitable when driven from high value electrical sources such as retail grid electricity or any small scale photovoltaics.
If you have electricity, sell the electricity, buy some methane, and reform the methane. It is a lot cheaper and throws away a lot less exergy.
This is remarkably comparable to our earlier electrical resistance heat example. Where your best solution involves converting a few higher value kilowatt hours into more lower value ones. Rather than fewer.
Even if you have a renewable and sustainable source of ultra low cost electricity, electrolysis can still easily convert it back down into a net energy sink. Individuals making their own "homebrew" hydrogen by electrolysis face other rude surprises. For openers, some to much of the produced "gas" may end up water vapor from dielectric heating. Safety issues are largely unappreciated and easily lead to Darwin Awards.
But the really big gotcha is trying to use stainless steel rather than costly platinized platinum electrodes. Because of the hydrogen overvoltage of iron found in most any electrochem textbook, and because of the dead-wrong low energy passivated surface, stainless slashes your possible efficiency by one-half or greater.